In the search for fuel economy in internal combustion powered vehicles, it has become common to provide some sort of clutch mechanism between the radiator fan and its prime mover. Some such mechanisms respond to temperature or rotational velocity, while others respond to high torque levels being transmitted to the fan to sense and act upon the need to reduce the coupling between the prime mover and the fan. These mechanisms allow a radiator fan to be bladed and pitched to provide sufficient cooling in stop-and-go traffic and yet pump no greater amounts of air through the radiator than is required at highway speeds.
One particular type of fan clutch mechanism includes a rotor mounted to rotate with respect to a surrounding case filled with a material such as silicon fluid which responds to shear forces in a nonlinear manner. The fluid causes lock-up between the rotor and the surrounding case at low torque levels but at higher torque levels releases the rotor from the case so that the two can spin relative to each other. There is, of course, energy expended in this operation which heats the silicon fluid and the surrounding mechanism. Heretofore, rotors and rotor cases have had dead zones where the fluid tends to remain creating hot spots which overheat the fluid causing it to break down and ultimately cause a premature failure of the clutch mechanism.
The design of various vehicles requires different mounting arrangements, diameters and spacing of the radiator fan. These differences caused by automotive design normally require that a large number of different fan clutch mechanism be stocked to supply the market. This is disadvantageous to both original equipment and aftermarket suppliers.
Therefore there has been a need to provide an easily manufactured fan clutch mechanism of the nonlinear fluid type which eliminates hot spots, provides adequate cooling, and accommodates installations with different physical dimension requirements.